1. Field of the Invention
The invention relates generally to an apparatus and method for amplifying baseband signals, and more specifically, to a power efficient method of providing for automatic gain control.
2. Discussion of the Related Art
A radio receiver in a wireless communication system is coupled to an antenna and includes a low-noise amplifier, programmable-gain amplifier, one or more intermediate frequency stages, a filtering stage, automatic gain control (AGC), and a baseband-processing stage. The low-noise amplifier receives transmitted RF signals via the antenna and amplifies them. The programmable-gain amplifier may further amplify the RF signals. The one or more intermediate frequency stages mix the amplified RF signals with one or more local reference signals to convert the amplified RF signal into baseband or intermediate frequency (IF) signals. The filtering stage filters the baseband or IF signals to attenuate unwanted out-of-band signals to produce filtered signals. The baseband-processing stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard employed.
The signal strength of a received RF signal may vary substantially (e.g., by 100 dB). Thus, the AGC adjusts the gain of the low-noise amplifier, the programmable-gain amplifier, and/or digital gain within the baseband-processing stage such that the receiver is sensitive enough to detect received low-power signals and, once detected, to adjust the gain of these components to achieve nominal signal level. The AGC may also be configured to decrease the gain of the low-noise amplifier, the programmable-gain amplifier, and/or the digital gain of the baseband-processing stage when the received signal is a strong signal. Gain control typically comprises varying the load of an amplification circuit, thus dissipating power.